1. Field of the Invention
The present invention relates to a semiconductor device including a connection terminal. In particular, the invention relates to a structure of a connection terminal of a display device including a pixel portion where pixels are arranged in matrix, and to a connection structure between an external terminal and a connection terminal of a display device.
2. Description of the Related Art
A display device may have a structure in which a flexible printed circuit is conductively connected to a display panel and a signal and power are supplied through the flexible printed circuit to the display panel.
For example, the display panel includes a pixel portion and a peripheral driver circuit for driving the pixel portion over a substrate, and the substrate is attached to an opposite substrate with a sealant in a sealing region. Then, at least the pixel portion is sealed with the substrate, the opposite substrate, and the sealant.
The substrate includes a region which is not overlapped with the opposite substrate, and a connection terminal portion is formed in that region. In the connection terminal portion, electrodes (connection pads) are arranged in stripes. Each of the electrodes is connected to a wire which is formed to extend outward from inside the sealing region.
As for the display panel, in the connection terminal portion, the electrode (connection pad) of a connection terminal is electrically connected to an electrode (FPC pad) of a flexible printed circuit terminal with an anisotropic conductive film or the like by thermocompression bonding.
Then, the signal and power supplied from the flexible printed circuit are supplied to a circuit over the substrate through each connection terminal and wire.
Here, a large amount of current flows through a power supply line (power supply path) including wires for supplying a power supply potential serving as a power source of the circuit over the substrate, a connection portion between the wires, a connection portion between the FPC terminal and the connection terminal over the substrate, and the like in order to operate the pixel, the peripheral driver circuit, and the like.
Therefore, there is a significant voltage drop in the power supply line if the resistance of the power supply line is high. Accordingly, the power supply potential supplied to the pixel and the peripheral driver circuit becomes lower than a desired power supply potential. As a result, a power supply potential inputted to the pixel and the peripheral driver circuit is decreased, which causes defective display.
Thus, References 1 and 2 disclose a structure in which power is supplied through a plurality of wires of a flexible printed circuit and wires connected to connection terminals to which a power supply potential serving as a power source of a circuit over a substrate is inputted, are connected to each other in a sealing region (Reference 1: Japanese Patent Laid-Open No. 2001-109395 and Reference 2: Japanese Patent Application Laid-Open No. 2001-102169).
However, even according to the above structure, if misalignment in a line width direction of the connection pad is caused in attachment of the substrate and the FPC, a connection area between the FPC terminal and the connection terminal becomes smaller and contact resistance is increased. In particular, an increase in contact resistance of the connection terminal to which a power supply potential serving as a power source is inputted is a cause of defective display.